Modify Subscription Balance for cach dues

I am looking for the best way to update a subscription balance through the REST API. The use case is we want to adjust the balance after they have been billed. Basically changing the balance due to 0. These are cash dues.

/subscription doesn't seem to update the field
/csSubscirptions GET works, POST is not allowed, and PUT results in "Does not have required permission. (O)"

Is there a path to update the subscription balance?

Thanks,
Randy